Display panel or portion thereof with a graphical user interface



FIG. 1 is a front view of a display panel or portion thereof with a graphical user interface showing a first embodiment of our design; and,

FIG. 2 is a second embodiment thereof.

The outermost broken line rectangle illustrates a display panel or portion thereof that forms no part of the claimed design. The remaining broken lines, including all text, illustrate portions of the graphical user interface and form no part of the claimed design. 

CLAIM The ornamental design for display panel or portion thereof with a graphical user interface, as shown and described. 